Chair back



FIG. 1 is an isometric view of a first embodiment of a chair back showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a back elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof;

FIG. 8 is an isometric view of a second embodiment of a chair back;

FIG. 9 is a front elevation view thereof;

FIG. 10 is a back elevation view thereof;

FIG. 11 is a left side elevation view thereof;

FIG. 12 is a right side elevation view thereof;

FIG. 13 is a top plan view thereof; and,

FIG. 14 is a bottom plan view thereof.

Those portions of the figures that are presented in broken lines merely illustrate the environment of the design and are not part of the claimed design. 

CLAIM The ornamental design for a chair back, as shown and described. 